Hey Riot, Is there any other information on the new "Non traditional marksman" ?

Unfortunately not, and they are not releasing roadmaps because with Volibear and Fiddlesticks reworks they're directly sharing development. We can only hope he will be released kinda soon but I'm not sure, they could delay the release. Generally they are released within 3 months span between them, but last years between (May 2018) and (December 2018) there were 5 months; that said, it was a year in which they focused more about reworks, so that may be the cause of that.

This year, though, and were released 14 May and 28 June, so the time for the release of new ADC could stretch more, if usually they release them with 3/4 months between them, then taking account of that they may indeed reveal him in 5 month, around November/December.

Sorry to disappoint you, but that's really a bad year to those who wanted regular new champion updates...